In a recent development of ours, we developed a joule effect electric melter aimed primarily at processes where consistency in properties like temperature and viscosity in a supply of molten material, such as molten glass, are important in forming a quality product. The melter is a shallow vertical melter that supplies molten material of uniform temperature to one or more product forming outlets located at the bottom of the melter. During operation, the melter establishes within the molten material of the melter a horizontal heating zone of substantially uniform temperature condition throughout.
When melting glass from a layer of raw batch formed on the surface of the molten body, molten glass in the melter rises to the molten glass/raw batch interface as a result of thermal currents caused by the heating zone. Molten glass moves across the upper surface of the molten body where it can easily degas. The thermal currents effect mixing and fining of the glass in such a way to promote uniform temperature of the molten glass in horizontal layers throughout the molten body. The result is a supply of glass of desired uniform temperature delivered at the entrance to the melter outlets.
The zone of the uniformly heated material is established in preferred form by operation of joule effect electrodes arranged in generally opposed spaced apart relationship. In a more specific sense, the electrodes are disposed in two groups, each in generally horizontal and laterally spaced apart relationship; the electrodes in each group are also arranged in opposed spaced apart relation. Means for supplying electrical current to the electrodes matches electrical current in each electrode with the particular spaced apart relationship of the electrodes to form the heating zone of substantially uniform temperature and thereby mix and move the molten glass to supply glass of uniform temperature to the entrance outlets of the melter.
The electrode power supply circuits of our recent development each equalize the flow of current through the individual electrodes disposed within the molten glass. The equalization of the flow of current in each electrode within the glass is produced by applying electrical power for driving either the electrodes directly or indirectly through additional cascaded current splitting inductors through the center tap of an inductor having ends which are respectfully coupled either directly to electrodes or to the center taps of the additional cascaded current splitting inductors. This recent development uses current splitters to equalize the flow of current through the individual electrodes. As a result, the only way to bias the temperature in any horizontal plane is by moving the electrodes in and out of the melter. This can be very difficult, especially with a high liquidus glass.